Warped MDF backsplash

[Nordberg]

Happy new year all,

I recently purchased laminated backsplash from B&Q. It is warped in both directions, which is preventing me from gluing it back to the wall.

Length ways is not really a problem, but width ways is a real headache.
I returned the first lot, but the replacements are just as bad.

Does anyone know of a quick effective way of reshaping? We deeply want to use this stuff, but dont want to screw it back.

Thanks in advance

 

[Scrit]

Once MDF is warped, that's it. Take it back. It has probably warped because of a defect in manufacturing OR it has got wet

Scrit

 

[nstreet]

Check it in store with a straight edge before purchasing, if you are able to that is.

How is it being transported and how are you storing it? You may have to prove that its not you causing the problem.

Have you checked that your wall is true as you are having the problem with more than one piece?

 

[Nordberg]

Cheers guys,

Its warped upon delivery and comes from manufacturer.
I'll send it back and tile the walls instead.

Cheers again

 

[hermes]

Once MDF is warped, that's it.

Scrit

Not true. I have had sheets delivered warped that have straightened out when laid flat for a while. Also I have often stacked offcuts up against a wall and they have warped but if I turn them around or put some weight on them they will flatten out again. I would suggest laying your splashback on a flat surface for a couple of days with some weight on it. I think it will probably sort itself out.

 

[Scrit]

Once MDF is warped, that's it.
Scrit

Not true. I have had sheets delivered warped that have straightened out when laid flat for a while.

I feel that there is a difference between warped laminated MDF upstand and raw MDF. The fact that worktops and upstands are only laminated on one side makes them inherently somewhat unstable and more likely to bow in one direction as they take-on moisture from the environment. This means that once manufactured they need to be handled and stored correctly. The word "warped" implies a twist along the length to my mind and that means there is some other form of tension in the item which is either the result of defective quality control in manufacturing or poor handling and storage subsequently. Once MDF has started to take on moisture it has a tendency to swell and then it really is scrap, IMO. Warping implies both moisture take-up and tensions and/or case-hardening of the substrate - neither acceptable as there will then be a tendency for the material to warp even further if it is machined. Raw MDF is much easier to straighten out as it will acclimatise by moisture loss/gain through both surfaces rather than the single surface of a laminated board. Yes, the warped board might straighten out if it's weighted down, but why waste time trying to correct a defect in what is obviously sub-standard material. If (nay, when) any of my timber merchants delivers, or rather attempts to deliver, defective materials like that he gets it straight back, followed by a verbal flea in his ear. Last year we rejected 5 or 6 loads - not bad out of 40+, I suppose.

Scrit

 

[hermes]

Worktops and upstands are (or should be) laminated on both sides to prevent an imbalance in moisture diffusion leading to bowing. This is called balancing. I have never seen a worktop that is laminated on one side only. Mdf can have tensions in it but this will usually result in movement perpendicular to the plane of cut edges, which means that the workpeice will still be flat although the edges will not be straight; as opposed to timber which can have tensions in any directions (hence the need for riving knives). I agree that warping normally suggests tension or imbalance rather than poor handling/storage but surely it's still worth a go?

 

[Scrit]

All the major worktops currently available in the UK (such as Resopal, Duropal, Prima, etc) are single side post-form laminated on a dense-ish particle board core. The underside generally has a layer of vapour barrier material (coated paper in effect) applied which has different moisture resistance properties to the laminate applied to the top/front edge, i.e. it is somewhat more permeable. I think that is partly why manufacturers bag their products in plastic and are fussy about storage conditions. Store a worktop in damp conditions and it will warp or bow. Store it racked upright without adequate support (like some merchants and DIY places do) and it will definitely warp given enough time. Once in place in a kitchen the underside of a worktop is sufficiently moisture resistant to be fit for purpose, however, it is noticeable that some major manufacturers of built-in dish washers and washing machines now supply additional vapour barriers to be applied to the underside of the worktop. If worktops are moisture resistant to the same extent both sides, why do that? Try sticking a couple of end offcuts from worktoips out in the winter rain, face and underside up for a month and you'll see what I mean about permeability.

The back edge of a worktop is similarly treated by the manufacturer with a sealing compound, and a good kitchen fitter will reseal this surface should he find it necessary scribe the rear of the worktop. He'll also do the same with a bonding agent in the mason's mitre joints.

All the upstands I've seen to date have a similar construction to worktops, and whilst weighting the item down may flatten it why should anyone have to accept sub-standard goods?

I have to admit that we get more problems of tension with raw particle board than with raw MDF - it results in a "banana" edge when strips are sawn on the panel saw. Any sheet showing those tendencies ends up getting machined on the CNC where we can clamp the so and so down so it won't move. Laminated materials such as MFC and MF-MDF tend to be more prone to this, especially the single-sided stuff used in retail stands and the like. But on the odd occasion we'll get a sheet which warps in both planes.

Scrit

 

[hermes]

Any sheet showing those tendencies ends up getting machined on the CNC where we can clamp the so and so down so it won't move.

Doesn't it just spring out of shape once you un-clamp though?

 

[Scrit]

Oh yes! But if it's so warped even the CNC can't pull it flat (about 3/4in over 6ft) then it's skip fodder. Most sheets like that (the ones I haven't rejected) get turned into small components where the warp isn't noticeable or where it can be "adjusted" out of the piece by the assembler. I expect a percentage of rejects at that point as well. Funny thing is that birch ply is much worse than MDF or particle board - it looks flat until you put it on the bed of the CNC and find it's to badly warped to hold down......

I don't like machining warped stuff, but as a percentage of what I do is contract CNC machining of other people's materials, I don't always have the choice.

Scrit